We propose a) to define the class, subclass, allotype, and hemolytic potential of IgG allo and autoantibodies encountered in the practice of blood transfusion and to correlate it with available clinical data. IgG subclassing will be done using IgG allotypic markers, which are subclass specific, on microtiter plates. The hemolytic potential of IgG antibodies will be tested using a human peritoneal macrophage phagocytosis assay. Clinical and experimental material needed to support these studies will be available to the applicant through the Regional Reference Laboratory and the Transfusion Service of the Milwaukee Blood Center and through collaborative arrangements with local hospitals who will supply ascites and lavage fluids from patients on peritoneal dialysis.